Internal-combustion engines – Combustion chamber means having fuel injection only – Combustible mixture stratification means
Reexamination Certificate
2001-09-14
2003-12-02
Yuen, Henry C. (Department: 3747)
Internal-combustion engines
Combustion chamber means having fuel injection only
Combustible mixture stratification means
C123S305000, C123S090150
Reexamination Certificate
active
06655345
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a valve timing controller, a valve timing control method and an engine control unit for an internal combustion engine, and more particularly, to a valve timing controller, a valve timing control method and an engine control unit for an internal combustion engine which is equipped with a valve timing changing mechanism for changing a valve timing for at least one of an intake valve and an exhaust valve such that the engine is operated in a combustion mode switched between a uniform combustion mode in which a fuel injection is performed during an intake stroke and a stratified combustion mode in which a fuel injection is performed in a compression stroke.
2. Description of the Prior Art
A conventional valve timing controller for an internal combustion engine of the type mentioned above is known, for example, from Laid-open Japanese Patent Application No. 7-301144. An internal combustion engine described in this document comprises a cam phase changing mechanism which changes the phase of an intake cam (hereinafter referred to as the “cam phase”) for a crank shaft as a valve timing changing mechanism. A change in the cam phase results in a change in valve timing of an intake valve, i.e., overlapping of the intake valve with an exhaust valve, and so on, thereby leading to a change in a filling efficiency and internal EGR. The disclosed valve timing controller sets a target cam phase in accordance with the engine rotational speed and a load represented by a throttle valve opening, so that the cam phase is controlled to reach the target cam phase, thereby achieving engine power suitable for the load of the internal combustion engine, and an improvement in the exhaust gas characteristics.
Another known valve timing controller for an internal combustion engine is described, for example, in Japanese Patent No. 2630632. The disclosed internal combustion engine comprises a cam profile switching mechanism, as a valve timing changing mechanism, which has an intake cam and an exhaust cam comprised of a lower speed cam and a higher speed cam, respectively, having different cam profiles from each other, such that the cam profile of each cam is switched between the lower speed cam and the higher speed cam. The switching of the cam profile causes a change in valve timings of the intake valve and the exhaust valve, i.e., the amount of valve lift and so on, resulting in an change in the filling efficiency. In this valve timing controller, the cam profile is switched based on the engine rotational speed and a basic fuel injection time which is calculated based on the engine rotational speed and a load represented by an intake pipe inner pressure, thereby providing engine power suitable for the load of the internal combustion engine.
Further, a recent internal engine, known as a direct injection type, directly injects a fuel into a cylinder, and is operated in a combustion mode which is switched between a uniform combustion mode and a stratified combustion mode in order to improve the fuel economy (see, for example, Laid-open Japanese Patent Application No. 11-
22508).
In this internal combustion engine, the stratified combustion mode is performed during an extremely low load operation such as idling, wherein a fuel injection is performed during an intake stroke with a throttle valve being substantially fully opened to supply a large amount of intake air into a cylinder for burning at an extremely leaner air/fuel ratio than the stoichiometric air/fuel ratio. On the other hand, the uniform combustion mode is performed during operations other than the extreme low load operation, wherein a fuel injection is performed during a compression stroke, and a throttle valve opening is controlled in accordance with a load represented by the engine rotational speed and an accelerator opening to control the amount of intake air for burning at a richer air/fuel ratio than the stratified combustion mode.
The foregoing cam phase changing mechanism and profile switching mechanism, though contributing to the improvement on the exhaust gas characteristics and engine power, may experience problems as follows, if they are employed in the conventional direct injection type internal combustion engine. As described above, the direct injection type internal combustion engine substantially fully opens the throttle valve during an extremely low load operation such as idling to perform the stratified combustion mode with a large amount of intake air supplied into a cylinder, so that the throttle valve opening, absolute intake pipe inner pressure, and amount of intake air become extremely large, causing the internal combustion engine to exhibit behaviors exactly opposite to those of a normal intake port injection type internal combustion engine. On the other hand, the conventional cam phase changing mechanism sets its target cam phase in accordance with the throttle valve opening as a parameter that represents the load, while the cam profile switching mechanism switches the cam profile in response to the intake pipe inner pressure that represents the load. Thus, if such a valve timing changing mechanism is simply combined in the conventional direct injection type internal combustion engine, a valve timing suitable for a load cannot be set in the stratified combustion mode, and as a result, the engine fails to ensure required engine power and internal EGR, resulting in deteriorated exhaust gas characteristics, fuel economy and operability.
OBJECT AND SUMMARY OF THE INVENTION
The present invention has been made to solve the problem as mentioned above, and its object is to provide a valve timing controller, a valve control method and an engine control unit suitable for use in a direct injection type internal combustion engine, which are capable of appropriately setting a valve timing in accordance with an engine load even in the stratified combustion mode.
To achieve the above object, according to a first aspect of the present invention, there is provided a valve timing controller for an internal combustion engine which is equipped with a valve timing changing mechanism for changing a valve timing of at least one of an intake valve and an exhaust valve so that the engine is operated in a combustion mode switched between a uniform combustion mode in which a fuel is injected into a cylinder during an intake stroke and a stratified combustion mode in which a fuel is injected into a cylinder in a compression stroke.
The valve timing controller according to the first aspect is characterized by comprising engine rotational speed detecting means for detecting a rotational speed of the internal combustion engine; accelerator pedal opening detecting means for detecting an opening of an accelerator pedal; required torque determining means for determining a required torque outputted by the internal combustion engine based on the detected engine rotational speed and accelerator pedal opening; and valve timing determining means for determining the valve timing in accordance with the determined required torque and the engine rotational speed.
The internal combustion engine is operated in the combustion mode which is switched between the uniform combustion mode in which a fuel is injected into a cylinder in an intake stroke and the stratified combustion mode in which the fuel is injected in a compression stroke. Also, according to the valve timing controller in the first aspect of the present invention, a required torque outputted by the internal combustion engine is determined based on the detected engine rotational speed and accelerator pedal opening, and a valve timing for the intake valve and/or the exhaust valve is determined in accordance with the determined required torque and engine rotational speed. In this way, the valve timing is determined in accordance with the required torque and engine rotational speed, while the required torque is determined as a torque which should be outputted by the internal combustion engine, based on the engine
Ehara Yasunori
Komoriya Isao
Ogawa Ken
Castro Arnold
Honda Giken Kogyo Kabushiki Kaisha
Lahive & Cockfield LLP
Yuen Henry C.
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